NFS: Fix a number of sparse warnings

Fix a number of "warning: symbol 'foo' was not declared. Should it be
static?" conditions.

Fix 2 cases of "warning: Using plain integer as NULL pointer"

fs/nfs/delegation.c:263:31: warning: restricted fmode_t degrades to integer
  - We want to allow upgrades to a WRITE delegation, but should otherwise
    consider servers that hand out duplicate delegations to be borken.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 2afe233..eb95f50 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -101,7 +101,7 @@
 /*
  * Prepare to bring up the NFSv4 callback service
  */
-struct svc_rqst *
+static struct svc_rqst *
 nfs4_callback_up(struct svc_serv *serv, struct rpc_xprt *xprt)
 {
 	int ret;
@@ -172,7 +172,7 @@
 /*
  * Bring up the NFSv4.1 callback service
  */
-struct svc_rqst *
+static struct svc_rqst *
 nfs41_callback_up(struct svc_serv *serv, struct rpc_xprt *xprt)
 {
 	struct svc_rqst *rqstp;